Antistatic treating composition for photographic film supports



1952 K. FAMULENER ETAL 2,584,337

ANTISTATIC TREATING COMPOSITION FOR PHOTOGRAPHIC FILM SUFPORTS Filed June 24, 1949' Legend Unwind, Leather Strap Broke Tinsel Heavy Nickel Roller with Broke Idle Nickel Rollers Windup Electromeler Gulvunometer Condenser Plate Shielded Cable C D E F G H I I'NVENTOR Keith Fomulener Hermon Hoerlln A OR Y8 Patented Feb. 5, 1952 ANTIS'IATIC TREATING ooMrosrrlou FOR PHOTQGRAPHIC FILM SUPPORTS- Keith Famulener, Owego, and Herman Hoerlin,

Binghamton, N. Y., assignors to General Aniline & Film Corporation, New York, N. Y., a

corporation of Delaware Application June 24, 1949, Serial No. 101,046

8 Claims. (Cl. 260-17) This invention relates to photographic film an particularly to a film treating composition havin anti-static properties. Considerable difficulty has been encountered in the manufacture of photographic filmdue to the accumulation of electrical charges on the film. In one step of the manufacture of photographic film, a film base is coated on one or both sides with a subbing composition which usually consists of a dispersion of gelatin in a suitable solvent or solvent mixture, so as to facilitate the adherence, or anchorage, of one or more of the photo-sensitive, non-curling or anti-halation layers. When such a laminate is wound into a tight roll and subsequently unwound, as during a coating operation, a considerable static electricity is generated and spark discharges readily occur. Such charges are spark discharges and after development of the coated and exposed-film, the results thereof show up as black streaks or lines, or as irregular fogged patterns in the emulsion layer. Attempts have been made to over come static in such laminates by the incorporation of substances into subbing compositions which are electrolytes or possess hygroscopic properties. The function of these substances is toimpart conductivity to the film and thus dissipate the charges before their accumulation leads .to local discharges. Many of these substances are incompatible with gelatin subbing compositions and introduce new manufacturing difliculties. P

Of the various supports currently utilized for the production of photographic film, those prepared from cellulose nitrate, cellulose acetate, cellulose propionate, cellulose butyrate, and mixed cellulose'esters have the greatest tendency to acquire rather high electrical charges. When the film is passed over another film surface or over highly polished metal surfaces, this tendency is especially pronounced for cellulose nitrate and is somewhat less for the other cellulose esters. Anti-static protection of cellulose nitrate-film supports is more difficult to achieve than of other cellulose organic acid ester film supports, such as. cellulose acetate, due to the much greater tendency of cellulose nitrate to acquire high negative charges. It has been known for the past twenty years that a thin layer of cellulose acetate over cellulose nitrate gives a fair static protection by reducing the susceptibility of untreated cellulose nitrate to about A, of the origi-' real value. This reduction, however, is not sufficient if. the film support so coated is utilized in a dry climate. A- further. reduction, ofsstatic 2 I susceptibility can be achieved by the use of special chemical compounds which essentially reduce the magnitude of the contact potential by means of a reduction of the area of actual contact.-

I Reduction of contact area reduces-adhesion be-: tween film sheets or between film and support; Consequently, the charge density produced Jay differences in contact potential is lowered.- In practice, the recognition of this principlehasled to surface roughening treatments which are ap-, plied to many kinds of commercial sheeting as, for example, to cellophaneused for wrapping, of merchandise and to photographic film supports. The treated surface is thus altered very slight' ly, in fact, so slightly, that the changecannot be detected by the 'naked eye. a

The roughening material must be deposited. on the surface in extremely minute quantities in order to beeffective. Such materials as barium sulfate, calcium silicate, finely divided chalk, and numerous clays, for example, bentonite 'areused as suspensoids in suitable media to roughen the surface slightly. All of these materials have the common disadvantage that they must be-used in colloidal suspensions suitable for slightly coating the plastic sheet. Such suspensionsare very;dif-s; ficult to prepare and are unstable, especially when the colloid is gelatin. Aqueous dispersions of such materials in gelatin solutions,-which are em loyed as subbing layers or carriers for antihalation dyes, are extremelyunstable and cannot be applied to the film support without the application of constant agitation. This agitation, though troublesome and time consuming, .is necessary to prevent the deposit ,of any minute quantities of roughening material tending to precipitate from the dispersion. r

The principal object of the present invention-is to provide photographic film supports which will possess improved anti-static properties.

Another object is to provide an improved film surface treating composition ha "ng anti-static properties.

A further object is to provide a, surface'treating' composition for photographic film supports which will readily permit the treated film to slip over other film and highly polished metal surf faces without creating static electrical charges.

Other objects and advantages will be apparent from the following disclosure.

- We have discovered that film supports espe-- cially photographic motion picture film prepared from cellulose derivatives, such as cellulose ni-- trate, cellulose acetate, cellulose propionate, cela lulose butyrate, cellulose acetatepropionatecelture thereof lulose acetatebutyrate, and the like, which fulfill the above objects, can be prepared by coating or swabbing a cellulosic film support itself or the cellulosic side of a finished photographic film with a solution of cellulose acetate, containing a small quantity of calcium silicate (CaSiOs, sold under the brand name of Silene E. F.), and a small quantity of poly-(methylene salicylic acid).

The calcium silicate, as above, has the purpose of reducing the area of surface contact. The reduction of contact area alone, though reducing the electrostatic charge density, is, however, not the only factor determiningthe static-susceptibility of cellulosic photographic film-support or sheeting.

The reduction of the magnitude of the contact potential between film and metal surfaces and the increase in surface conductivity are of even greater importance. We have discovered that the mixture of the calcium'silicate with the celluloseiacetate' and .thetpoly (methylene salicylic acid) i'sF far more. effective than the cellulose acetateor calcium silicate layers alone or mix- For example, it has been found that a small. quantity, approximately 1% by weight or less, of: calcium silicate and poly- (methylene salicylic" acid) dispersed in cellulose acetateismany times more'efficient to prevent static tlranthesame quantity of calcium silicate dispersedfm cellulose acetate as the carrier. ltiwas'also: discovered that the mixture of cellulose acetate and calcium silicate with poly- (me-thylene salicylic: acid) has slippage characteristicsisuperior to thoseof cellulose acetate or calcium "silicate layers. alone or mixture thereof.

As pointed out above, thecoating of a cellulose'nitrate film base with a solution of cellulose acetate gives a'fairstatic protection. The coatlng ofa' cellulose acetate'film base with a solution ofcellulose' nitrate is without significance. Wh'ezr calcium silicate; is-added to a solution of cellulose nitrate, the relative'static susceptibility is approxirnately less than that of untreated cellulosenitrate. Treating cellulose nitrate film Base witli a suspension of calcium silicate in alcoh'oFreduces'the' relative static susceptibility to a similar'extentl V Before-proceeding with the practical aspects ofth'e'presentinvention; it will'be desirable and helpful" to brieflydescribe the apparatus employed in evaluating" the"static' susceptibility of a treated'film,

V By reference to'the drawing, which is' selfexplanatory, it will be observed that it consists essentially of 5 afilm rewinding machine. This machine is operated as follows: The test film, after leaving unwind A is first discharged completelyjby means of tinsel bars B to prevent disturbing efie cts'by residual charges. When going over roller: C, the film acquires a certain amount ofi'ch'arge and the-corresponding charge of oppo- "site polarityis permitted to'fiow from the roller surfacethrough galvanometer G to ground. The

4 fiection of which is directly related to the charge on the film.

The electric charges generated are measured and the relative static susceptibility determined. l"he galvanometer and electrometer data singly, or average after: proper weighting, permit the evaluation of the static susceptibility of a film sample in arbitrary units. With constants of the circuit known, it is also possible to calculate the charge density per unit surface area quantitatively in absolute units. The latter conversion is'not, however, required for most practical applications and only relative values of static susceptibility will be given in the following examples. An arbitrary value of -100 is usually assigned to the untreated sample or type.

In practicing the present invention, a dispersion of calcium silicate in an aralkyl alcohol, such as benzyl alcohol, phenylethyl alcohol, phenylpropyl alcohol, cinnamic alcohol, saligenin and the like is first prepared by grinding a mixture of calcium silicate and alcohol in a labora-' tory ball mill for a period of 8: hours. The amount of calcium silicate tobeemployed may range from 5 to 30% by weight of. the alcohol. Although the quantity of calcium silicate is not critical, it has been found that a 20% alcohol dispersion of calcium silicate is satisfactory for most practical purposes.

From 1 to 10 cc. of the-20% alcohol dispersion of calcium silicate as above prepared; is incorporated with constant agitation into a cellulose acetate dope solution to make the volume upto 1000 cc. The dope consists essentially of a 5-15% solution of cellulose acetate, ranging from to 56% of combined acetic acid, in the usual organic solvents, or mixtures thereof, such as, for ex ample, methanol, ethanol, benzyl alcohol, acetone, ethylene dichloride, and the like. The solvent or solvent mixture actually employed must be such that it will have a solvent or at least a' softening or swelling action on the cellulose derivamagnitude. of. this current i directly related to V the magnitudeofthe charge carried away by the film. After passing idle rollers D, the film is wound on windup. ro1l ..E.' Halfway between roll -ers '13,. there is a fiat-condenser plate H'mounted parallel to the filmsurface at a distance of approximately 1.25 cm, The'condenser plate is tivefilm base so as" to stick or anchor the antistatic coating composition upon'thei area of the base which has been softened onswollen.

It will be appreciatedthat eachdifierent type of cellulose ester requires aislightly different solvent or solvent combination. For example, with a celluloseacetate, a ketone, such as acetone, or a mixture of a low molecularweight alcohol, e; g., methanol, ethanol, and the like, and acetone'may be employed. The ratio of alcohol to: acetone ranges from about 30-60% to -25%, respectively. With cellulose'acetate-propionate film base, an alkyl ester, such as, for example, methyl acetate, ethyl acetate, butyl acetate, and the like, either. alone or with methanol, may beefiectively employed. It maybe noted at this point that the nature of the organic solvent or solvent mixture is immaterial so long as it. wets or'b'ites into the. cellulose film material, and theterm sol ven as used in the claims. should bevconstrued. Since the materials'suitable for cellulose derivative film bases and their solvent properties-are known, no difliculty is presented in selecting a suitable solvent or solvent mixture foruse in: the cellulose acetate dope compositions.

Before making up the cellulose acetate dope solution, containing dispersed calcium silicate, up to volume, a small quantity. of poly-(methylene salicylic acid) ranging from 0.05 to 1% by weight, preferably 0.1-0.5" by weight, isincorporated into the dope 1 solution. Theprepared' solutionmay be filtered if. desired. to remove'small agglomeratesof calcium silicate.

The poly-(methylene salicylic acid) is prepared by. placing a mixture of 1000 grams of salicylic acid, 1715 ml. of formaldehyde (40%) and 377 ml. of hydrochloric acid (conc.) in a liter round-bottom two-neck flask (or a 5-liter single-neck flask with two-way adapter) equipped with stirrer and condenser. The flask is heated on a steam bath, in which it should be at least halfway submerged, or proper insulation should be provided to insure eflicient heating.

After heating for one hour, reflux action will become quite violent, and steam should be turned oil, applying cold towels, if necessary, to calm the reaction. When the mixture ceases to reflux of its own heat of reaction, the steam is turned on again. At the end of the second hour, a white plastic mass'should be present. It may float on the surface of the liquid. The reaction mixture is poured into a 4-liter beaker. The plastic mass is allowed to settle and the supernatant liquid decanted.

The white plastic mass is washed once with water, and then dissolved in come. NI-hOI-I (28%) The solution is diluted in a large crock to 4-5 times the volume with water. Conc. HCl is added with stirring, until the solution is strongly acidic. At this point, a colloidal mass of resin may be formed. Steam is passed through the mass to flocculate the resin and facilitate filtration. The resin is chilled with ice until the mixture is, at least, at room temperature. It is then filtered, washed with water and again dissolved-now in 2-3 1. of 6 N NaOH.

The solution is diluted as before and the resin is precipitated with conc. HCl. On appearance of a colloidal mass, steam is passed through. The resin is chilled with ice, filtered, washed with water (until only slightly acidic of a pH of 3-4) and dried in air for approximately 3 days, or until no moisture appears to be present. It is then placed in the oven at 80-90 C. for approximately 3 days. When no odor of formaldehyde is evident, the resin is removed -from the oven and ground to a fine yellow powder.

100% yield=1069 g.

Example I A strip of 35 mm. cellulose nitrate film support was coated with the following composition:

Parts 20% dispersion of calcium silicate in benzyl alcohol 5 Poly-(methylene salicylic acid) l solution of cellulose acetate in 30 parts' of methanol and 70 parts of'ethylene di chloride .50 Methanol 400 Ethylene dichloride 500 Benzyl alcohol 44 If the steaming is omitted, a pseudo- After the anti-static layer had dried, the coated film strip was tested for static susceptibility with an untreated strip of cellulose nitrate as a control and the following data obtained:

Relative Static Susceptibility Untreated Strip l00 Treated Strip 1 Example]! Example I was repeated with the exception that the following composition was employed:

' Parts 20% dispersion of calcium silicate in benzyl The treated and untreated cellulose nitrate film strips were tested for static susceptibility and the following data obtained:

Relative Static Susceptibility Untreated Strip -l00 Treated Strip +1 Example III A strip of cellulose acetate film support was coated with the following composition:

Parts 20% dispersion of calcium silicate in benzyl alcohol 5 Poly-(methylene salicylic acid) 2 10% solution of cellulose acetate in acetone 15 50/50 mixture of acetone and ethyl alcohol 978 After the anti-static coating layer had dried, the coated film strip was tested with an untreated strip of cellulose acetate film as a control, and the following data obtained:

Relative Static Susceptibility Untreated Strip l00 Treated Strip -2 In addition to the foregoing specific examples, comparative experimental data are shown in the following table:

Relative Static Suscepti- ,bility Film Base I Coating None 20% Dispersion of calcium silicate in benzyl alcohol. 20% Dispersion of calcium silicate in benzyl alcohol+cellulose nitrate. Cellulose acetate 20% Dispersion of calcium silicate in benzyl alco-. hold-cellulose acetate in methanol-acetone mixture.

Cellulose Nitrate As shown in the above table, a coating compo- :sition containing a dispersion of calcium silicate alone or with a cellulose ester is only slightly effective in reducingstatic charges. It is evident that a substantially improved antistatic protection is obtained by the mixture of cellulose acetate with calcium silicate and poly-(methylene salicylic acid).

The extent of the anti-static protection was even more pronounced when film samples provided with anti-static layers and carrying high speed photographic emulsions were compared for their performance in an ordinary motion picture camera. The film samples were allowed to run through these cameras in absolute darkness and were then developed in an ordinary black and white developer, fixed and washed. The developed samples which had untreated cellulose nitrate and acetate films as a base showed very strong static marks. The samples coated on a film base treated with calcium silicate displayed moderately strong static marks.

Only minute traces of static marks could be found on a motion picture film coated withthe composition of Example I, whereas no static marks could be found on a photographic film coated with the composition of Example II.

The protective nature of the coating containing cellulose acetate, calcium silicate and poly- (methylene salicylic acid) became most pronounced when tested at low humidities in comparison with the samples containing calcium silicate alone.

It is to be understood that while benzyl alcohol has been specifically disclosed as the dispersing medium for the calcium silicate in the above examples, any of the other aralkyl alcohols mentioned previously may be utilized with equal effect. The reason that benzyl alcohol has been specifically utilized is because of its relative cheapness and commercial availability.

The treated photographic film bases produced according to the present invention in addition. to preventing the accumulation of static charges when unwound during a coating operation were found to be very satisfactory from the standpoint of physical requirements, such as high strength, flexibility, slippage, and good water resistance.

The invention is not limited to the treatment of finished photographic motion picture film nor the base utilized in the manufacture of such film, but is also useful in treating the back surface of any photographic roll or sheet film having a basis of a cellulose derivative. Its particular advantage, however, is in the treatment of finished motion picture negative film so as to protect the exposed and processed film against the accumulation of dust and dirt particles which occur when the film is moved through a printer or projector. I

It will be understood that where in the claims appended hereto the term film is used, that such term is intended to include roll film support and finished roll film.

It is. not intended that the invention be limited by any of the specific examples which have been given merely for the sake of illustration nor by any theory as to the mechanism of the treating operation, since variations of the invention will become apparent to workers in the art. Our invention is limited only by the following claims.

We claim:

1. An anti-static cellulose acetate composition suitable for treating a film of a cellulose ester which comprises --15% solution-of cellulose acetate in a solvent for said. film and containing poly-(methylene salicylic acid) and calcium silicate dispersed in an aralkyl alcohol of the benzene series.

2. An anti-static cellulose acetate composition suitable for the treating of a film of a cellulose ester which consists of the following constituents:

Parts by weight 20% dispersion of calcium silicate in benzyl alcohol 5 Poly-(methylene salicylic acid) 1 10% solution of cellulose acetate in 30 parts of methanol and '70 parts of ethylene dichloride 50 Methanol 400 Ethylene dichloride 500 Benzyl alcohol 44 3. An anti-static cellulose acetate composition suitable for the treating of a film of a cellulose ester which consists of the following constituents:

Parts by weight 20% dispersion of calcium silicate in benzyl alcohol 2.5 Poly-(methylene salicylic acid) 3 10% solution of cellulose acetate in 30 parts of methanol and 70 parts of ethylene dichloride l5 Methanol 375 Ethylene dichloride 582.5 Benzyl alcohol 22 l. An anti-static cellulose acetate composition suitable for the treating of a film of a cellulose ester which consists of the following constituents:

7 Parts by weight 20% dispersion of calcium silicate in benzyl alcohol 5 Poly-(methylene salicylic acid) 2 10% solution of cellulose acetate in acetone 15 50/50 mixture of acetone and ethyl alcohol 978 Parts by weight 20% dispersion of calcium silicate in benzyl alcohol 5 Poly-(methylene salicylic acid)- 1 10% solution of cellulose acetate in 30 parts of methanol and 70 parts of ethylene dichloride 5O Methanol 400 Ethylene dichloride 500 Benzyl alcohol 44 7. A process of improving the anti-static and slippage characteristics of a film of. a cellulose ester which comprises treating one surface offsaid film with a composition of the following constituents:

Parts by weight 20% dispersion of calcium silicate in benzyl alcohol 2. Poly-(methylene salicylic acid) 3 10% solution of cellulose acetate in 30 parts of methanol and 70 parts of ethylene dichloride 15 Methanol 3'75 Ethylene dichloride 582.5 Benzyl alcohol 22 8. A process of improving the anti-static and slippage characteristics of a film of a cellulose ester which comprises treating one surface of said film with a composition consisting of the following constituents:

I Parts by weight 20% dispersion of calcium silicate in benzyl alcohol 5 Fwy-(methylene salicylic acid) 2 10% solution of cellulose acetate in acetone" 15 50/50 mixture of acetone and ethyl alcohoL- 978 KEITH FAMULENER. HERMAN HOERLIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. AN ANTI-STATIC CELLULOSE ACETATE COMPOSITION SUITABLE FOR TREATING A FILM OF A CELLULOSE ESTER WHICH COMPRISES 5-15% SOLUTION OF CELLULOSE ACETATE IN A SOLVENT FOR SAID FILM AND CONTAINING POLY-(METHYLENE SALICYCLIC ACID) AND CALCIUM SILICATE DISPERSED IN AN ARALKYL ALCOHOL OF THE BENZENE SERIES. 